1. Field of the Invention
The invention disclosed in this specification and the like relates to semiconductor devices.
2. Description of the Related Art
In recent years, flat panel displays such as liquid crystal displays have been widespread. In each of pixels provided in the row direction and the column direction in a display device such as a flat panel display, a transistor serving as a switching element, a liquid crystal element electrically connected to the transistor, and a capacitor connected to the liquid crystal element in parallel are provided.
As a semiconductor material for forming a semiconductor film of the transistor, a silicon semiconductor such as amorphous silicon or polysilicon (polycrystalline silicon) is generally used.
Besides, metal oxides having semiconductor characteristics (hereinafter referred to as oxide semiconductors) can be used for semiconductor films of transistors.
For example, techniques for forming transistors including zinc oxide or an In—Ga—Zn-based oxide semiconductor are disclosed (see Patent Documents 1 and 2).